A Weak Cable Backbone Can Paralyze a Project

As part of a new construction project, you install a camera with a fixed focal length lens. What happens when the user isn’t happy with the resulting view? You change the lens. What if you add a card reader to a system and there is a protocol compatibility issue? You swap out the reader. Fortunately, these problems have relatively simple solutions. But there’s one aspect of such a project that usually isn’t so easily remedied: the cable infrastructure. Imagine what could happen if you selected the wrong type of cable for your infrastructure. What if you went to your distributor and asked for 50,000 feet of coax for a video system, or 10,000 feet of fiber, and were given something inappropriate for the application? Or let’s say the wrong type of cable is specified. Then what do you do?

We all know what happens next. Everything from finger-pointing to lawsuits is possible. But the bottom line is once the walls go up it’s extremely difficult, if not impossible, to pull it all out and start over. Most distributors are educated and know what the right materials are for the job, but mistakes happen. Sometimes overzealous purchasing people might try to save a few dollars and use substitutes, not understanding the impact that decision might have at a technology level.

Whatever the reason, it is important to understand that mistakes in infrastructure can have lasting consequences. In some cases, these consequences will have to be tolerated for many years. That’s why you need to be sure what you’re putting in meets the requirements and is the right cable for the application. Whether that system requires coaxial cable, fiber optics or unshielded twisted-pair (UTP) wire, basic considerations must be identified and resolved to ensure a quality installation with which any security integrator would be proud to be associated.

Coax Is Still Very Popular, But It Is Not All Created Equal

First up is the old standby — coax. According to John Cowley, business development manager for CommScope Enterprise Solutions of Hickory, N.C., while the cabling solutions provider anticipates 10- to 20-percent growth in converged systems during the next few years, “We have not seen a tremendous move away from coax yet.” It appears there is some life in the old round, copper-core cable yet.

If you do decide to use coax, it is very important to remember not all of it is created equal. There are several different types, not all of which are right for every application.

If you come out of the audio-visual (A/V) world, you are familiar with most forms of coaxial cable. MATV, CATV and satellite systems all use some type of coax. Did you know, however, that the cable used in those systems is generally not appropriate for CCTV systems?

This disparity generally comes from the different frequencies the signals use to travel down the cable. For instance, CATV video uses anywhere between 50MHz to 990MHz; CCTV signals are found down between 5MHz and 10MHz. These frequencies cause the signals to behave in different ways. The higher frequencies of the CATV signal tend to travel down the skin of the center conductor, while the lower CCTV signal moves closer to the core.

Why does this matter? Because most CATV-rated cables have copper-clad aluminum center conductors, since those signals stay at the outside of the conductor. The most important thing to look for when choosing coax for a CCTV installation is a solid copper center conductor to provide the best path for the signal to travel.

You also need to choose coax with a minimum 95-percent coverage, copper braid for a shield. The use of aluminum foil, or tape-shielded, cable is not recommended for CCTV applications, again because the copper is a much better conductor for the return path.

Another item to be aware of is impedance. Our CCTV equipment likes to see a nominal impedance of 75O (ohms). Several things, such as termination of devices, affect this but the cable itself also needs to be rated at 75O. Coax for other applications such as antennas and networking are often rated at 50O and are not appropriate for CCTV.

As long as cameras and monitoring/recording devices are manufactured with BNC connections on the back, there will be a life for coax. It is premature to declare the complete death of this workhorse, although as convergence continues to take a greater hold on our industry it will lose its place to more updated and scalable technologies, such as fiber.

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